1. Field of the Invention
The present invention relates in general to continuously variable transmissions, and more particularly, to continuously variable transmissions of a friction roller type.
2. Description of the Prior Art
Japanese Patent First Provisional Publication No. 2-163553 shows one conventional continuously variable transmission of the above-mentioned type. The transmission shown in this publication comprises generally a torque converter, a lock-up clutch, a forward/reverse movement switching device, a toroidal disc type speed change device, a countershaft and an output shaft. These parts except the countershaft are arranged on a common axis, and the countershaft is arranged in parallel with the common axis. Torque from an engine is transmitted through the torque converter (or the lock-up clutch), the forward/reverse movement switching device, the toroidal disc type speed change device and the countershaft to the output shaft. Between the speed change device and the countershaft, there are arranged two constantly engaged gears, and between the countershaft and the output shaft, there are arranged three constantly engaged gears including one idler gear. The idler gear is employed for matching the rotation direction of the output shaft with that of the engine.
SEA Paper 751180 shows in FIG. 7 another conventional continuously variable transmission of such type. The transmission comprises generally a hydraulic clutch, an input shaft on which the clutch is coaxially arranged, a toroidal disc type speed change device, a planetary reduction gear and an output shaft. These parts except the hydraulic clutch and the input shaft are arranged on a common axis, and the hydraulic clutch and the input shaft are arranged in parallel with the common axis. This means that the output shaft is arranged offset to the input shaft. Between the input shaft and the speed change device, there are arranged two constantly engaged gears. These two gears are so designed as to increase the speed of rotation applied to the speed change device. Thus, the torque applied to the speed change device is lowered.
Due to their inherent constructions, the above-mentioned two transmissions have the following drawbacks.
That is, in the transmission of Japanese Patent First Provisional Publication No. 2-163553, the engine torque is substantially directly inputted to the toroidal disc type speed change device through the torque converter or the lock-up clutch. This means increasing the torque receiving capacity of the speed change device and thus brings about enlargement in size of the transmission. Furthermore, usage of the three gears between the countershaft and the output shaft promotes the size enlargement.
In the transmission of the SAE Paper, so-called "torque lowering gears" are arranged upstream of the speed change device for lowering the torque applied to the same. Thus, one of the drawbacks encountered in the former transmission is solved. However, in the latter transmission, the input shaft and the output shaft are arranged offset to each other. This means that the size of the transmission is inevitably increased by a degree corresponding to the offset.